Field of the Invention
Applicants' invention relates to a device for shutting off motorized rigging. More particularly, it relates to a limit switch that confines the motion of a stage curtain to a predetermined position by deactivating the motor that drives the rigging.
Background Information
Theater drapes and stage curtains are large pieces of cloth that are designed to mask backstage areas of a theater from spectators or change acoustic values of a room. They are designed for a variety of specific purposes and come in several types.
There are several parts typically used in the curtain assemblies, generally including:                Cable Drum: Helically grooved drums that neatly wrap the cable lifting battens. Multiple drums may be used, and supported by a line shaft assembly. They are spaced to properly support the batten or load.        Chain Track: Chain and supported track combination used to move curtains or scenery.        Computerized Control Systems: Control systems that allow precise position of battens for each scene. They can also track speed, height, and travel of the battens, allowing the changes between scenes to be recorded into memory, and repeated in the exactly the same manner.        Drum Winches: Motorized winch with a single drum long enough to accommodate all of the lift lines required to support a batten. The helically grooved drum wraps the cable neatly in a single layer, to avoid damage to the cable and to keep all lines lifting equally. Winches can be located on the grid, catwalks, or in a separate motor platform. Head and loft blocks may be used to direct the lift lines to the batten.        Gear Motor: The combined gearbox, motor and brake provide speed reduction, power, and mechanical braking in the smallest space.        Limit Switch: Rotary switch geared to rotation of the shaft of the motor. When the switch turns to the appointed spot, it cuts power to the motor. Limit switches can have a number of positions to allow for high trim, low trim, or over travel.        Line Shaft Winch: An assembly consisting of the gear motor, and cable drums connected with a steel shaft. Each lift line uses a separate cable drum. The entire load is transferred through the winch frame assembly to the structure, eliminating horizontal loads, and the need for head blocks and loft blocks. The line shaft winch is ideal for situations where there is not much space nor structure to accommodate the horizontal loads.        Manual Controls: Simple push button controls to allow visual positioning of battens with motorized systems. All buttons release when they are not being pushed. All controls include an emergency stop that kills power to the motors.        Point Hoists: When great flexibility is required, a set of spot lines, or point hoists work together to support and operate a batten or load. Small portable point hoists can be attached to a grid. Larger units can be used with loft blocks to position the lift line appropriately.        
The rigging assemblies also have several standard components, generally including:                Batten: A metal pipe, generally 1½″ in diameter attached to the onstage lines from a rigging system. Scenery, draperies, or lighting equipment is attached to the batten.        Counterweight Arbor: A metal carriage that holds the counterbalancing weights used in a counterweight rigging system.        Counterweight Arbor Guides: A device that attaches to a counterweight arbor and engages the guide rails to control the movement of the arbor. Guides employ low friction sliding materials or roller elements. Arbors are generally guided by a fixed (Tee-Bar or JBar) guides, but can also be guided with wire rope.        Hand Line: The rope pulled by the rigging operator to raise and lower the counterweight rigging battens.        Headblock: A multisheave block with two or more pulley wheels, used to change the direction of all the cables that support the batten. It is located directly above the arbor, pin rail, or hoist.        Lift Lines: Cables or ropes attached to the counterweight arbor at the offstage end, reeved through head blocks, and loft blocks and are terminated to the batten or load over the stage.        Loading Bridge: A catwalk or walkway that is suspended just below the grid where the counterweights are loaded onto or removed off from the arbor.        Loft Block: A grooved pulley mounted on top of the grid, used to change the direction in which the cable travels from the head block to the batten.        Mule Block: A grooved pulley mounted on top of the grid, used to redirect the lift line in another direction.        Outrigger Batten: A batten mounted in a fixed position to support locking rail work lights and protect the counterweight rigging equipment from contact with scenic elements.        Rope Lock: A positioning device, located on the locking rail, which grips or releases the hand line of a counterweight set.        Tension/Floor Block: A grooved pulley mounted at the floor level of the counterweight set. The floor block removes slack from the hand line and prevents it from twisting in its travel.        Trim Chain: Short chain used to attach the lift lines to the battens. The chain is attached to the lift line, wraps around the batten, and then is attached back to itself or the lift line with a shackle.        
The curtains are hung from battens or tracks. Often, it is desirable to have the curtains move outwardly along the battens. Heavyweight velour is the current industry standard for these types of curtains. Due to the heavyweight material and the size of the curtains, they tend to be extremely heavy. In order to move the curtains, they are generally hung on a chain or cable suspended by pulleys, while the chain is moved by an electric motor. The chain moves in a circuit so at the terminal ends it generally takes a tight turn about a terminal sprocket or pulley and then follows the batten back along the track of the curtain. It can be extremely important that the curtain stop before getting into a position that causes excessive torque on the motor and damage to the motor, curtains, battens, or chains. Therefore, it's important that the curtain motor to have a stop system that limits movement of the curtains at a desired or necessary point. Likewise, there may be a point at which the users wish the curtains to be stopped for use, aesthetic, or other purposes.
Stopping the massive theater drapes has generally been done using a limit switch with a rotational counter, a limit switch that the curtain contacts to activate, or simply a person as a spotter to hit a stop button.